Solar cells and solar modules convert sunlight into electricity. These electronic devices have been traditionally fabricated using silicon (Si) as a light-absorbing, semiconducting material in a relatively expensive production process. To make solar cells more economically viable, solar cell device architectures have been developed that can inexpensively make use of thin-film, preferably non-silicon, light-absorbing semiconductor materials such as but not limited to copper-indium-gallium-selenide (CIGS).
Many traditional thin-film CIGS manufacturing techniques use co-evaporation or other vacuum based deposition techniques where all of the components of the final semiconductor material are formed in one step. In particular for co-evaporation, the material is grown from the bottom-up, with content carefully controlled as the material is grown. Although material content through the depth of the layer is more controllable, this one step type fabrication process is typically a time consuming process.
By contrast, multi-step fabrication techniques which involve deposition and then a subsequent anneal in one or more steps in a group VIA or other reactive environment can sometimes be a higher throughput process that, unfortunately, is more susceptible to migration and/or phase separation of material during fabrication. In one nonlimiting example, gallium content in depth of the initially deposited material is subsequently much different through the depth of the final semiconductor layer as much of gallium is pushed to bottom of the layer in the final semiconductor material.
One problem faced with thin-film type solar cells is the difficulty in cost effectively creating solar cells with higher conversion efficiencies, more on par with the efficiencies of their crystalline silicon counterparts. Improved techniques are desired so that improved thin film photovoltaic absorbers are formed.